$ { \left[\begin{array}{r}{1} \\ {3} \\ {1}\end{array}\right]+\left[\begin{array}{r}{-2} \\ {1} \\ {2}\end{array}\right] = {?} } $
Answer: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{r}{1}+{-2} \\ {3}+{1} \\ {1}+{2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{-1} \\ {4} \\ {3}\end{array}\right]}$